1. Field of the Invention
The present invention relates to an electronic device able to suppress propagation of vibration caused by piezoelectric and electrostriction phenomena and thereby reduce noise, more particularly relates to a ceramic capacitor used for an audio circuit or other circuit sensitive to noise or used for a smoothing capacitor for a switching power source.
2. Description of the Related Art
There have been remarkable advances in technology for reducing the thickness of layers and technology for increasing the number of layers of multilayer ceramic capacitors in recent years. Capacitors having high electrostatic capacities comparable to those of aluminum electrolytic capacitors have been marketed. As the ceramic materials for forming the stacks of such multilayer ceramic capacitors, barium titanate and other ferroelectric materials having relatively high dielectric constants are generally used.
Such ferroelectric materials, however, have piezoelectric and electrostriction properties, so stress and mechanical strain are caused when the ferroelectric materials are subjected to an electric field. Further, when an AC voltage is applied to a multilayer ceramic capacitor using such a ferroelectric material, the stress and mechanical strain caused in synchronization with the frequency of the AC voltage is manifested as vibration. This vibration is transmitted from the terminal electrodes of the multilayer ceramic capacitor to the board side.
For example, in a conventional multilayer ceramic capacitor, two types of internal electrodes are alternately arranged in the stack. The ends of the stack are provided with a pair of terminal electrodes connecting to these internal electrodes. These terminal electrodes are connected to interconnect patterns on the board by for example solder, whereby the multilayer ceramic capacitor is mounted on the board.
When applying an AC voltage to a multilayer ceramic capacitor, stresses Fx, Fy, and Fz occur at the main body of the multilayer ceramic capacitor along the X-, Y-, and Z-directions, whereby vibration occurs. This vibration is transmitted from the terminal electrodes to the board, whereby the board as a whole becomes a sound reflecting surface and a buzzing sound is liable to be generated as noise. This buzzing noise is sometimes noise of an audible frequency (20 to 20000 Hz). The buzzing noise is unpleasant to humans in some cases. Countermeasures are therefore required.
Further, such buzzing noise has a detrimental effect on the performance and quality of apparatuses having audio circuits or other circuits sensitive to noise. Accordingly, use of multilayer ceramic capacitors using ferroelectric materials for such apparatuses has generally been avoided.
Note that for example as shown in Japanese Unexamined Patent Publication(A) No. 2000-306764, Japanese Unexamined Patent Publication(A) No. 11-74147, Japanese Unexamined Patent Publication(A) No. 11-74147, Japanese Unexamined Patent Publication(A) No. 2002-231569, Japanese Unexamined Patent Publication(A) No. 2001-185446, and Japanese Unexamined Patent Publication(A) No. 2000-235931, technology for preventing vibration by the elastic deformation of the external terminals of multilayer ceramic capacitors has been disclosed.
However, in such multilayer ceramic capacitors, the fact is that the external terminals are high in rigidity and a sufficient effect of preventing vibration has not been obtained.